1. Field of the Invention
The present invention relates to an organic-inorganic composite material usable as an electrochromic display device and photoelectric conversion device, and a method for producing the organic-inorganic composite material, and a functional electrode and functional device using the organic-inorganic composite material.
2. Description of the Related Art
Recently, much research effort has been made to electronic paper as an electronic medium that is expected to displace paper. In contrast to conventional displays including CRTs and liquid crystal displays (LCDs), electronic paper is required to have the following characteristics: (1) being a flexible reflective display device; (2) high white reflectance and contrast ratio; (3) high definition display; (4) memory effect in display; (5) low-voltage drive capability; (6) slimness and lightness; (7) inexpensiveness, and the like. For example, an electrochromic display device utilizing color development/color erasure of an electrochromic compound has been researched and developed in wide ranges such as material development, device design and the like as a candidate for electronic paper, because it is a reflective display device, has memory effect and can be driven at low voltage. Various colors can be developed according to material structure, thus it is expected to be used also as a multiple color display device.
As a material for realizing an electronic device such as those typified by electronic paper, an organic-inorganic composite material has been actively researched. For example, Japanese Patent Application Laid-Open (JP-A) No. 2000-506629 proposes a material in which an electrochromic compound is adsorbed on a nanocrystalline layer deposited on an electrode. In JP-A No. 2000-506629, a terminal of a functional organic material such as acidic groups of a carboxylic acid, salicylic acid and the like is adsorbed to hydroxyl groups of inorganic fine particles, thus an organic compound can be adsorbed on the inorganic fine particles, but its bonding force is not so strong that the bonds between the organic compound and the inorganic fine particles are easily broken when an electrochromic device is produced, repeatedly used, or used under alkaline conditions, and the device has poor durability.
On the other hand, a dye-sensitized solar cell, in which a colored organic compound having photosensitization function is adsorbed to inorganic fine particles, proposed by Grätzel et al. (see Nature, 353, 737 (1991)), has the same configuration as the electrochromic device. However, as it stands, there is a problem of poor durability as with the electrochromic device.